There are certain advantages to use polyolefin backing materials, especially orientated polypropylene. The orientated polypropylene (OPP) as the backing material makes it possible to use high labeling speeds compared to paper materials because OPP has good tensile strength. The process is also more reliable compared to that with paper materials, which can easily break. In contrast to both paper and polyester, the backing material of orientated polypropylene is cheaper, and the backing films of OPP can be substantially thinner than that of polyester, which means more label material per volume.
The use of the OPP film as a backing web is known from WO 96/30886. In that publication, either OPP, paper, or polyester is used as the backing web of a peelable web. The backing web comprises a release layer. A hot melt adhesive is applied on one surface of the peelable web, and the webs are attached to each other. The peelable web may be a paper web.
In plastic containers, such as cans or bottles, are often used plastic labels provided with printed information. Such containers are used especially for packaging cosmetic products, which require pleasant appearance, and thus the label should preferably be except the printed area as invisible as possible compared to the surface to which it is attached. In practice, the aforesaid fact means that the label is of plastic material, and it is either transparent or possesses the same colour as the container. Polyolefin labels are especially suitable for this use because they are clear, and possible to process as thin films.
Publication WO 99/55517 discloses a clear or opaque label product, which comprises a polypropylene or polyethylene film as a top material, a release liner, and a pressure-sensitive adhesive between the top material and the release liner. The pressure-sensitive adhesive can be UV-curable. The release liner is of polyester, and the pressure-sensitive adhesive is applied on the release liner.
The problem of the prior label products is that there is no way to produce a laminate in which both the face material and the backing material are of polyolefin. Polyolefines do not resist temperature very well, and therefore adhesives, which have to be applied and/or cured with heat, must be applied on a surface other than the polyolefin surface. Especially thin backing materials of polyolefin, such as OPP, are very vulnerable to process conditions. Some adhesives are used with polyolefins but the use of water-based adhesives or solvent-based adhesives is not advantageous because due to restricted process temperature it takes a long time to dry the adhesive, and still problems with stretchy backing film occur, which causes problems in cutting and punching. Further, solvent-based adhesives are harmful, and need recovery and/or burning systems. Rubber-based hot melt adhesives are unsuitable for plastic laminates, and further, they are also unsuitable for use with transparent face materials because they do not resist UV light.